Automatic transmission

ABSTRACT

A mesh-type automatic transmission includes a power input shaft for introducing power of an engine, a plurality of transmission gears, a plurality of cogged clutches, a power output shaft for outputting driving force, a counter shaft, and a plurality of counter gears, for transmitting power of the engine to the power output shaft by rotating the power input shaft with the power of the engine, rotating the counter shaft, and transmitting rotation of the counter shaft to the power output shaft with automatic gear change by engaging and disengaging the cogged clutches to one of the transmission gears corresponding to the speed. The counter shaft is provided with an assist mechanism for transmitting rotational force of the power input shaft to the power output shaft by transmitting rotation of the counter shaft via the assist gear, during the period of disengagement of a gear to the engagement of a new gear during gear change.

FIELD OF THE INVENTION

The present invention relates to an automatic transmission.

BACKGROUND ART

Heretofore, there is known an automatic transmission using atransmission device of a conventional manual transmission mechanism,that is, a mesh gear type transmission mechanism, which is also providedwith a clutch for engaging and disengaging the engine with thetransmission device, and an actuator for moving the clutch to engage anddisengage each gear with the power output shaft, and which performsautomatic transmission (gear change) by controlling the hydraulicpressure on the actuator for the engagement and disengagement of theclutch.

In a conventional automatic transmission thus constituted, there existsa condition where the cogged clutch is engaged to none of the gears,which is so-called a neutral condition.

In such neutral condition where the cogged clutch is engaged to none ofthe gears during gear change from first gear to second gear, from secondgear to third gear, from third gear to fourth gear, and from fourth gearto fifth gear, the driver might encounter a sort of shock as if thevehicle decelerated even when the vehicle is actually accelerating,because the cogged clutch during gear change is left unmeshed with anyof the gears and therefore the acceleration power is not transmitted tothe power output axle.

Accordingly, it is an object of the present invention to provide anautomatic transmission that relieves the shock caused by the engagementand disengagement of the clutch during acceleration.

SUMMARY OF THE INVENTION

In order to achieve the above-mentioned object, in one aspect, thepresent invention provides a mesh type automatic transmission where, forthe purpose of transmitting power of the engine to a power output shaft,the power of the engine rotates a power input shaft, which causesadditional rotation of a counter shaft, which has, in turn, its rotationcammed to various gears by transmission gears respectively engaging anddisengaging with a cogged clutch for automatic velocity control, whichis transmitted to the power output shaft by a counter gear, and thecounter shaft includes an assist mechanism for transmitting rotationalforce of the power input shaft to the power output shaft withoutengagement of the cogged clutch with any of the transmission gearsduring the time when the cogged clutch is switching gears.

In order to achieve the above-mentioned object, according to anotheraspect, the assist mechanism according to the present invention isplaced at an end of the counter shaft facing the rear lateral side of avehicle body.

In order to achieve the above-mentioned object, according to stillanother aspect, the assist mechanism according to the present inventionis placed below a horizontal plane in which a central axis of the poweroutput shaft lies.

In order to achieve the above-mentioned object, according to a furtheraspect, the assist mechanism according to the present invention isdesigned to respond to a command to switch the cogged clutch and startengagement with the power input/output shafts prior to a completedisengagement of the cogged clutch from the current transmission gear,effect the engagement by engine torque to transmit the rotational forcefrom the power input shaft to the power output shaft upon a completerelease of the cogged clutch from the current transmission gear, andrespond to another switch command and disengage from the powerinput/output shafts upon engagement of cogged clutch with the newlyspecified transmission gear.

In order to achieve the above-mentioned object, in yet another aspect,the assist mechanism according to the present invention is comprised ofan assist clutch and an output gear, the assist clutch including aclutch plate fixed to the counter shaft and rotating along with thecounter shaft and an assist gear rotatably placed on the counter shaftfor pressing the clutch plate to transmit rotation of the clutch plate,the output gear being meshed with the assist gear of the assist clutchand fixed to the power output shaft for attaining the highest gear,whereby the assist mechanism responds to an assist command to transmitrotation of the clutch plate through the assist gear and the output gearto the power output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall structural view of an embodiment of an automatictransmission according to the present invention;

FIG. 2 is an enlarged view of an assist mechanism shown in FIG. 1;

FIG. 3 is a right side view of the automatic transmission in FIG. 1;

FIG. 4 is a view indicating a position where the automatic transmissionof the present invention is provided in a vehicle body;

FIG. 5 is a view explaining engagement and disengagement of the assistmechanism during gear change;

FIG. 6 is a view explaining engagement and disengagement of the assistmechanism during gear change;

FIG. 7 is a view explaining engagement and disengagement of the assistmechanism during gear change;

FIG. 8 depicts details of an exemplary overall structure of a vehicleemploying the automatic transmission of the present invention;

FIG. 9 is a flowchart illustrating commanded assist clutch transmissiontorque control during gear change;

FIG. 10 is a flowchart illustrating arithmetic operation control forcomputing a control command for the engine;

FIG. 11 is a timing chart illustrating a state of controls during gearchange;

FIG. 12 is a diagram illustrating the relation between an assist gearratio and a transmission enabled zone;

FIG. 13 is a diagram illustrating the relation between the assist gearratio and a power output shaft torque;

FIG. 14 is a diagram illustrating the relation between the assist gearratio and a differential torque;

FIG. 15 is a diagram illustrating the relation between the assist gearratio and a differential rotation frequency of an assist clutch;

FIG. 16 is a table showing comparison information with the referenceassist gear ratio;

FIG. 17 shows an embodiment of the overall structure of the automatictransmission of the present invention with the reference assist gearratio at the third gear; and

FIG. 18 shows another embodiment of the overall structure of theautomatic transmission of the present invention with the referenceassist gear ratio at the third gear.

BEST MODE FOR IMPLEMENTING THE INVENTION

With reference to FIGS. 1 to 7, preferred embodiments of an automatictransmission will now be described in accordance with the presentinvention.

FIG. 1 is an overall structural view of an embodiment of the automatictransmission according to the present invention, FIG. 2 is an enlargedview of an assist mechanism shown in FIG. 1, FIG. 3 is a right side viewof the automatic transmission shown in FIG. 1, FIG. 4 is a viewindicating the position where the automatic transmission of the presentinvention is provided in a vehicle body, and FIG. 5 through FIG. 7 areviews explaining engagement and disengagement of the assist mechanismduring gear change.

In FIG. 1, an automatic transmission 3 is housed in a transmission case30. In the transmission case 30, a power input shaft 300 rotated byengaging with a main drive clutch (not shown) is rotatably supported. Adrive gear 301 is provided at the end of the power input shaft 300facing the rear of the vehicle. The drive gear 301 rotates along withthe rotation of the power input shaft 300. Also, in an opposite side ofthe drive gear 301, a power output shaft 323 is rotatably provided on anextension of the power input shaft 300 without contacting the drive gear301, so that the axial center of the power output shaft 323 coincideswith the axial center of the power input shaft 300.

Also, below the power output shaft 323, a counter shaft 315 is rotatablysupported in parallel with the power output shaft 323. A counter drivegear 314 is fixed to an end of the counter shaft 315 facing the front ofthe vehicle body. The counter drive gear 314 meshes with the drive gear301, and is constituted so as to rotate with the drive gear 301. Thedrive gear 301 rotates with the rotation of the power input shaft 300,when the rotation of the engine is transmitted to the power input shaft300 by the engagement of the main drive clutch. It is constituted sothat when the drive gear 301 rotates, the counter drive gear 314 meshingwith the drive gear 301 rotates, and the counter shaft 315 fixed withthe counter drive gear 314 rotates. A counter third gear 316 is fixed tothe counter shaft 315 at its rearward along the vehicle body at apredetermined interval from the counter drive gear 314, and a countersecond gear 317 is also fixed to the same at a predetermined intervalfrom the counter third gear 316.

Also, to the rearward side along the vehicle body from the countersecond gear 317, there is fixed a counter first gear 318 at apredetermined interval from the counter second gear 317. Moreover, tothe rearward side of the vehicle body from the counter first gear 318,there is fixed a counter fifth gear 322 at a predetermined interval fromthe counter first gear 318.

The counter third gear 316 is meshed with a third gear 303, which isrotatably provided to the power output shaft 323. To the power outputshaft 323, there is provided a cogged clutch 302 between the third gear303 and the drive gear 301. The cogged clutch 302 is connected to thepower output shaft 323. That is, the cogged clutch 302 is slidablyconnected onto the power output shaft 323 and transmits the output ofthe power input shaft 300 to the power output shaft 323 by shifting thecogged clutch 302 so as to engage the cogged clutch 302 with the drivegear 301 (fourth speed position), or transmits the rotation of the powerinput shaft 300 to the power output shaft 323 via the counter third gear316 with the speed changed by shifting the cogged clutch 302 so as toengage the cogged clutch 302 with the third gear 303.

Also, the counter second gear 317 is meshed with a second gear 304,which is rotatably provided to the power output shaft 323. Moreover, thecounter first gear 318 is meshed with a first gear 306, which isrotatably provided to the power output shaft 323. To the power outputshaft 323, there is provided and connected a cogged clutch 305 betweenthe second gear 304 and the first gear 306. The cogged clutch 305 isslidable along on the power output shaft 323 and transmits the output ofthe power input shaft 300 via the counter second gear 317 with the speedchanged by shifting the cogged clutch 305 in the frontward direction ofthe vehicle body so as to connect with the second gear 304. Also, thecogged clutch 305 transmits the output of the power input shaft 300 viathe counter first gear 318 with the speed changed by shifting the coggedclutch 305 in the rearward direction of the vehicle body so as toconnect with the first gear 306. Therefore, even if rotation of thecounter shaft 315 causes the counter second gear 317 and the counterfirst gear 318 to rotate, the rotational force of the counter shaft 315is not output to the power shaft 323 as long as the cogged clutch 305 isnot meshed.

The operation of the cogged clutch 302 and the cogged clutch 305 isperformed by moving a striking rod 311 via a striking arm 312, byoperating the actuator of a shift select controller 5. The shift selectcontroller 5 operates the switching of the transmission gear, selectedfrom the accelerator command value output based on the amount of theaccelerator pedal depressed by the driver and the current speed of theautomobile.

At the rearward side of the vehicle body of the counter shaft 315 thanan intermediate plate 307, there is fixed a reverse counter gear 319.The reverse counter gear 319 operates when the vehicle moves backward.The reverse counter gear 319 is meshed with a reverse idler gear 320rotatably mounted to a reverse shaft 321, as shown in FIG. 3. Thereverse idler gear 320 is constantly rotated by the reverse counter gear319 rotating together with the counter shaft 315. A reverse gear 309 isrotatably provided to the power output shaft 323. To the frontward ofthe vehicle from the reverse gear 309, a cogged clutch 308 is providedand connected to the power output shaft 323.

Moreover, the counter fifth gear 322 is fixed to the rearward side ofthe vehicle body at a predetermined interval from the reverse countergear 319 on the counter shaft 315. The counter fifth gear 322 mesheswith a fifth gear 310, which is rotatably provided to the power outputshaft 323. The fifth gear 310 transmits the output of the power inputshaft 300 to the power output shaft 323 by engaging with the coggedclutch 308 provided and connected to the power output shaft 323. Thatis, the cogged clutch 308 is slidable along on the power output shaft323 and transmits the output of the power input shaft 300 via thecounter fifth gear 322 with the speed changed, by shifting the coggedclutch 308 to the rearward direction of the vehicle body, so as toconnect with the fifth gear 310. Therefore, even when the counter fifthgear 322 rotates along with the counter shaft 315, the rotational forceof the counter shaft 315 is not output to the power output shaft 323, aslong as the cogged clutch 308 is not meshed.

Also, the position of the counter shaft 315 is formed so that it ispositioned below the horizontal plane where the central axis of thepower output shaft 323 lies, as shown in FIG. 3. The position of thecounter shaft 315 is formed so that it is positioned below thehorizontal plane where the central axis of the power output shaft 323lies. It should be positioned below the horizontal surface including thecentral axis of the power output shaft 323 and the position is notnecessarily specified. However, it is ideally constituted so that thecentral axis of the counter shaft 315 is positioned perpendicular to thecentral axis of the power output shaft 323, that is, on the connection Aof the central axis. In this way, the assist mechanism could be providedto the lowermost portion of the transmission case 30, so that the innerspace of the transmission case could effectively be used, and thecooling effect from the oil could be expected. Moreover, the assistmechanism could be mounted to a position without hindering the access tothe gear oil injection hole.

Moreover, at the lateral end portion of the counter shaft 315 on itsrearward side along the vehicle body, there is provided an assist clutch6, as shown in FIG. 2. In this position of the assist clutch 6 at thelateral end portion of the counter shaft 315 in its rearward side alongthe vehicle body, repairing, exchanging and the like, of the assistclutch 6 could be performed with ease, when abnormality occurs to theassist clutch 6.

Furthermore, by mounting the assist clutch 6 to the counter shaft 315,the size of the transmission case 30 could be reduced, and the structureof the automatic transmission 3 could be miniaturized. Furthermore, byproviding the assist clutch 6 at the lateral rearward end portion of thecounter shaft 315 of the vehicle, assembly could be facilitated.

According to the present embodiment, the location of the assist clutch 6is the lateral end portion of the counter shaft 315 at the rear side ofthe car body. However, the assist clutch 6 may not necessarily belocated to the lateral end portion of the counter shaft 315 at therearward side along the vehicle body, as long as it is provided on thecounter shaft 315. In order to enable repairing, exchanging and the likeof the assist clutch 6 when abnormality occurs to the assist clutch 6,it is ideal to provide the assist clutch 6 to the counter shaft 315 atits lateral end portion in its rearward along the vehicle body.

Also, the assist clutch 6 has a clutch plate 61 fixed to the countershaft 315, as shown in FIG. 5. The clutch plate 61 is constantlyrotating with the rotation of the counter shaft 315. Opposing to theclutch plate 61, an assist gear 324 provided with a rotating plate whichpresses against the clutch plate 61 is rotatably provided on the countershaft 315. The assist gear 324 is meshed with an assist output gear 324.The assist gear 324 is constantly rotated by the assist output gear 325which is rotated by the rotation of the power output shaft 323, as longas the clutch plate 61 and the assist gear 324 are disengaged. When theclutch plate 61 and the assist gear 324 are engaged, the rotationalforce of the counter shaft 315 is transmitted to the assist gear 324 viathe clutch plate 61, thereby rotating the assist gear 324, and rotatingthe assist output gear 325 by the rotation of the assist gear, so as toprovide assist force of the assist clutch 6 to the power output shaft323.

As seen from above, the assist gear 324 is rotatably provided to thecounter shaft 315 to rotate independent of the counter shaft 315.Because the clutch plate 61 is fixed to the counter shaft 315 providedwith the assist clutch 6, and the rotation of the counter shaft 315 istransmitted to the power output shaft 323 via the clutch plate 61through the assist gear 324 and the assist output gear 325, byconnecting the clutch plate 61 and the assist gear 324 from operatingthe assist clutch 6, the rotational force of the power input shaft 300could be assisted to the power output shaft 323 by the operation of theassist clutch 6, when rotation of the power input shaft 300 is nottransmitted to the power output shaft 323 during the period ofdisengagement of the currently engaged gear and the engagement of a newgear at gear change (during neutral). Therefore, the shock originatedduring the period of disengagement of the currently engaged gear and theengagement of the new gear at the gear change could be eliminated.

The switching of the reverse gear 309 is performed by the cogged clutch308. The cogged clutch 308 is constituted so as to slide freely on thepower output shaft 323. By shifting the cogged clutch 308 to thefrontward direction of the car body, the reverse gear 309 connected tothe power output shaft 323 and the reverse idler gear 320 are meshed,and the rotation of the reverse idler gear 320 is transmitted to thepower output shaft 323 via the reverse gear 309. When the cogged clutch308 is engaged with the reverse gear 309, the vehicle moves backward.

The automatic transmission 3 thus constituted is provided at the centerof the car body 1 in the moving direction, as is shown in FIG. 4. In thedrawing, reference number 2 denotes the engine, 4 denotes the main driveclutch, 5 denotes the shift select controller, 6 denotes the assistclutch, 7 denotes a hydraulic unit, and 8 denotes an indicator.

Next, the operation of the automatic transmission 3 will be explained.

First, when the driver turns on the starting switch in the state wherethe range lever is in the parking (P) position or in the neutral (N)position, the starter motor rotates and starts the engine 2. When thedriver moves the range lever to the drive range (D) position afterstarting of the engine 2, the shift select controller 5 operates theactuator under the command from the range lever, and shifts the coggedclutch 305 connected to the power output shaft 323 to the rearwarddirection of the vehicle, in order to engage with the first gear 306.With the engagement of the cogged clutch 305 with the first gear 306,the cogged clutch 305, the first gear 306 and the counter first gear 318are meshed.

At this point, the rotation of the power input shaft 300 is transmittedto the counter shaft 315 from the drive gear 301 via the counter drivegear 314 to rotate the counter shaft 315, and the rotation of thecounter shaft 315 is transmitted to the first gear 306 via the counterfirst gear 318. The power output shaft 323 rotates with the rotation ofthe first gear 306, thereby rotating the wheels.

In the state where the cogged clutch 305 is shifted to the rearwarddirection of the vehicle to engage with the first gear 306, the powerinput shaft 300 is not rotating, so that the drive gear 301 fixed to thepower input shaft 300 does not rotate. Therefore, the counter drive gear314 fixed to the counter shaft 315 and meshed to the drive gear 301 doesnot rotate. Also, because the counter shaft 315 does not rotate, thecounter first gear 318 fixed to the counter shaft 315 does not rotate.

When the driver operates the accelerator pedal, the main drive clutch 4is gradually engaged, in order to start rotation of the power inputshaft 300. The rotation of the power input shaft 300 rotates the drivegear 301, which is transmitted to the counter drive gear 314 meshed tothe drive gear 301 so as to rotate the counter shaft 315. The rotationof the counter shaft 315 rotates the counter first gear 318, which istransmitted to the first gear 306, so as to rotate the power outputshaft 323 engaged by the cogged clutch 305, thereby rotating the wheels.

When the driver depresses the accelerator pedal further, revolution ofthe engine and the car speed increases further. The accelerator commandvalue corresponding to the amount of the accelerator pedal depressed isinput to the control device, in order to decide whether the gearposition is the first gear 306 or the second gear 304, from theaccelerator command value and the car speed. When it is determined asbeing within the range of the second gear 304, a drive command is outputfrom the control device to the shift select controller 5. The actuatoroperates based on the drive command of the shift select controller 5, toshift the cogged clutch 305 connected to the power output shaft 323 tothe frontward direction of the vehicle to disengage the mesh with thefirst gear 306, and to further shift the cogged clutch 305 to thefrontward direction of the vehicle to engage with the second gear 304.When changing from the first gear 306 to the second gear 304, the coggedclutch 305 becomes temporarily disengaged from either the first gear 306or the second gear 304, between disengagement with the first gear 306and the engagement with the second gear 304. At this point, the driverfeels no acceleration being effected in spite of depressing theaccelerator pedal, or even rather encounters a shock of temporarydeceleration. The assist mechanism works to damp the shock of the driverduring gear change.

The assist mechanism at gear change when the gear is switched operatesas is shown in FIG. 5 through FIG. 7. The case where the gear isswitched from the second gear 304 to the third gear 303 will beexplained below as an example.

FIG. 5 shows the condition where the cogged clutch 305 is shifted to thefrontward direction of the vehicle and engaged with the second gear 304.

The condition shown in FIG. 5 is the condition where the second gear 304rotated by meshing with the counter second gear 317, which rotatestogether with the rotation of the counter shaft 315 and which is fixedto the counter shaft 315, is engaged with the power output shaft 323 byshifting the cogged clutch 305 to the frontward direction of the carbody, so that the rotational force of the power input shaft 300 istransmitted to the power output shaft 323 via the counter second gear317. That is, the rotational force of the power input shaft 300 istransmitted to the counter shaft 315 from the drive gear 301 via thecounter drive gear 314 to rotate the counter shaft 315, and the rotationof the counter shaft 315 is transmitted with the speed changed via thecounter second gear 317. At this point, the assist output gear 325 isrotated by the rotation of the power output shaft 323, and the assistgear 324 meshing with the assist output gear 325 is idling above thecounter shaft 315 from the rotation of the counter assist gear 324.

In such state, the assist gear 324 meshing with the assist output gear325 fixed to the power output shaft 323 is not engaged with the countershaft 315, as is shown in FIG. 5. The assist gear 324 is rotating on thecounter shaft 315 independently of the counter shaft 315, from therotation of the power output shaft 323 via the assist output gear 325.The assist gear 324 is constantly idling above the counter shaft 315, aslong as the power output shaft 323 is rotating, so that the rotationalforce transmitted to the power input shaft 300 from a fly wheel 330 viathe main drive clutch 4 is not provided to the assist gear 324.

When the operation command for changing from the second gear 304 to thethird gear 303 is output under such condition, the cogged clutch 305 isshifted to the rearward direction of the vehicle to disengage from thesecond gear 304, and the cogged clutch 302 is shifted to the rearwarddirection of the vehicle to engage with the third gear 303. When thegear change operation command is output, the command for operating theassist clutch 6 is output, so that the assist clutch 6 operates beforethe cogged clutch 305 disengages from the second gear 304, and engageswith the assist gear 324 by pressing against the clutch plate 61 withhydraulic pressure, as is shown in FIG. 6. The engagement of the coggedclutch 305 and the second gear 304 is disengaged thereafter. With suchoperation, the rotation of the clutch plate 61 is transmitted to theassist output gear 325 via the assist gear 324. FIG. 6 shows thenon-engaged condition where the cogged clutch 305 is disengaged from thesecond gear 304, and the cogged clutch 302 is also disengaged from thethird gear 303.

With the rotation of the assist gear 324, the rotation of the countershaft 315 is transmitted to the assist output gear 325 meshing with theassist gear 324. The clutch plate 61 engaged to the assist gear 324 isfixed to the counter shaft 315, so that the assist clutch 6 operates.When the clutch plate 61 and the assist gear 324 engages, the rotationof the clutch plate 61 rotated by the counter shaft 315 is transmittedto the assist output gear 325 meshing with the assist gear 324 via theassist gear 324, and is transmitted to the power output shaft 323 fixedwith the assist output gear 325 via the assist output gear 325.

As is seen from above, even when the non-engaged condition where neitherthe second gear 304 nor the third gear 303 is engaged temporarily existsduring transition from the second gear 304 to the third gear 303, therotation transmitted to the power input shaft 300 from the fly wheel 330via the main drive clutch 4 is transmitted from the drive gear 301 viathe counter drive gear 314, the counter shaft 315, the clutch plate 61,the assist gear 324, the assist output gear 325, and the power outputshaft 323, with the operation of the assist clutch 6. Therefore,obstructing of operation of the drive force to the power output shaft323 during non-engaged condition at gear change could be prevented,relieving the shock at gear change.

After the assist mechanism performs assistance, the cogged clutch 302 isshifted to the rearward direction of the vehicle to engage with thethird gear 303, and the assist clutch 6 operates to disengage the assistgear 324 from the clutch plate 61.

FIG. 7 shows the condition where the cogged clutch 305 is held at theneutral position, the cogged clutch 302 is engaged with the third gear303, and the assist gear 324 and the clutch plate 61 is disengaged. Asis shown in the drawing, when the cogged clutch 302 is engaged with thethird gear 303, the rotation of the power input shaft 300 is transmittedto the counter shaft 315 from the drive gear 301 via the counter drivegear 314, and the rotation of the counter shaft 315 is transmitted tothe third gear 303 via the counter third gear 316, and to the poweroutput shaft 323 via the third gear 303 engaged with the power outputshaft 323 by the cogged clutch 302.

When the driver attempts to increase the speed by depressing theaccelerator pedal further, the revolution of the engine increases, andthe increased revolution increases the rotation of the counter shaft 315via the drive gear 301. When the speed of the vehicle (car speed)reaches the driving limit in third gear 303, the control device detectsthat the gear position is within the range of the fourth gear 301 (drivegear) from the accelerator command value and the car speed, and outputsthe drive command from the control device to the shift select controller5. By operating the actuator, the cogged clutch 302 connected to thepower output shaft 323 is shifted to the frontward direction of thevehicle to disengage the mesh with the third gear 303, and the coggedclutch 302 is shifted further to the frontward direction of the vehicleto engage with the fourth gear 301 (drive gear). When the gear ischanged from the third gear 303 to the fourth gear 301 (drive gear), therotation of the power input shaft 300 is transmitted directly to thepower output shaft 323 from the drive gear 301, so that the power outputshaft 323 is rotated by the rotation of the power input shaft 300itself.

When the gear is changed from the third gear 303 to the fourth gear 301,there temporarily exists a non-engaged condition where neither the thirdgear 303 nor the fourth gear 301 is connected with the power outputshaft 323. Under the non-engaged condition, the driver feels noacceleration from depressing the accelerator pedal, and shock oftemporary deceleration is caused during gear change. The assist clutch 6operates in order to relieve the shock to the driver during gear change,as is mentioned above. The operation of the assist clutch 6 is the sameas is mentioned above.

Likewise, when the gear is changed from the fourth gear 301 to the fifthgear 310, there temporarily exists a non-engaged condition where neitherthe fourth gear 301 nor the fifth gear 310 is connected with the poweroutput shaft 323. Under the non-engaged condition, the driver feels noacceleration from depressing the accelerator pedal, and shock oftemporary deceleration is caused during gear change. The assist clutch 6operates in order to relieve the shock of the driver during gear change,as is mentioned above. The operation of the assist clutch 6 is the sameas is mentioned above.

When the driver slackens the accelerator pedal when the transmissiongear is in the position of the third gear 303, the speed of the vehiclereduces, and car speed is slowed down. Then, the control device detectsthat the gear position entered the range of the second gear 302 from therange of the third gear 303 from the accelerator command value and thecar speed, and outputs drive command from the control device to theshift select controller S. By operating the actuator, the cogged clutch302 connected to the power output shaft 323 is shifted to the frontwarddirection of the vehicle to disengage the mesh with the third gear 303.At the same time, the cogged clutch 305 connected to the power outputshaft 323 and in a position of non-engagement is shifted to thefrontward direction of the vehicle to engage with the second gear 304.With the engagement of the cogged clutch 305 with the second gear 304,the cogged clutch 305, the second gear 304, and the counter second gear317 are meshed.

Therefore, the rotation of the power input shaft 300 rotates the countershaft 315 from the drive gear 301 via the counter drive gear 314, andthe rotation of the counter shaft 315 is transmitted to the second gear304 via the counter second gear 317. With the rotation of the secondgear 304, the power output shaft 323 rotates in proportion to the secondgear 304 with the rotation of the second gear 304, so that car speed isslowed down. When the speed of the vehicle is lowered from the slackingof the accelerator pedal by the driver, in the condition where the gearis the third gear 303, the gear change is performed under slow-down ofthe car speed so that there exists no shock from gear change, even whenthere occurs a temporary non-engaged condition during gear change fromthe third gear 303 to the second gear 304. Therefore, the assistmechanism does not perform assistance.

Also, during the gear change from the second gear 304 to the first gear306, the speed of the vehicle is lowered by the slacking of theaccelerator pedal by the driver, as is the case with the gear changefrom the third gear 303 to the second gear 304, so there exists no shockfrom gear change, even when there occurs a temporary non-engagedcondition during gear change from the second gear 304 to the first gear306. Therefore, the assist mechanism does not perform assistance.

The transmission theory of the present invention has been outlinedheretofore. Next, controls over the automatic transmission of thepresent invention will be explained in detail.

FIG. 8 is a detailed depiction of an exemplary overall structure usingthe automatic transmission according to the present invention.

A control unit comprises an electronically controlled throttle controlunit 401 used to control an electronically controlled throttle 103, anengine control unit 402 used to control an engine, a transmissioncontrol unit 403 controlling a gearbox, and an indicator control unit412 adapted to provide the operator with the driving conditions andcontrol statuses.

An engine 101 shares the electronically controlled throttle 103 toadjust engine torque and is comprised of various sensors including anengine sensor 102 for a detection of an engine rotation frequency, andvarious actuators. The engine 101 is under control of the engine controlunit 402. The electronically controlled throttle 103 is under control ofthe electronically controlled throttle control unit 401.

The automatic transmission 3 places the actuators 203, 221, 222 and 226under control of the transmission control unit 403.

The transmission control unit 403 receives automobile sensor signalsfrom various sensors like an accelerator pedal sensor 406 for sensingthe amount of depression of the accelerator pedal, an impedance switch407 for detecting the position of a shift lever, a power output shaftrevolution sensor 300 for detecting the rotation frequency of the poweroutput shaft, a mode switch 408 switching the mode from automatictransmission to manual transmission and vice versa, an accelerationswitch 408 used to shift the gear up by one stage during the manualtransmission mode, a deceleration switch 410 used to shift the gear downby one stage during the manual transmission mode, and so forth. Variousindicators such as a lamp 411 are added thereto. The transmissioncontrol unit 403 is connected to the engine control unit 402, theelectronically controlled throttle control unit 401, and the indicatorcontrol unit 412 by communication bus 404 such as CAN (control areanetwork).

The transmission control unit 403 determines states of the operationfrom the signals received to give adequate controls over the state ofthe clutch upon initial driving, the gear position, and so on. Thetransmission control unit 403 places the electronically controlledthrottle 103 under control of the electronically controlled throttlecontrol unit 401 to inhibit excessive puffing of the engine 101 in thecourse of gear shift during the automatic transmission mode. Thetransmission control unit 403 controls the electronically controlledthrottle 103 and the assist clutch 6 for smooth transition oftransmitted torque from immediately before the gear shift to immediatelyafter the completion of the gear shift. In addition to that, a correctedvalue of ignition timing is sent from the transmission control unit 403to the engine control unit 402 to optimize the ignition timing. Theindicator control unit 412 enables various indications of the drivingstate and control conditions by means of letters and symbols on adisplay, vocal guidance, etc. Thereby, smooth driving with reducedshocks associated with gear shift is realized.

Referring now to FIGS. 9 to 11, a control method upon gear shift will beexplained in a control system for a vehicle incorporated with theautomatic transmission of this embodiment.

The control method follows and executes a program that is stored in amicrocomputer built in the transmission control unit 403 and the like.

FIG. 9 is a flow chart illustrating a commanded assist clutchtransmission torque control upon gear shift from the first gear to thesecond gear. The program starts with an interruption of a fixed interval(e.g., 10 ms) and executes a command sequence as follows:

-   -   Step 501 Read in a change-speed instruction Ss;    -   Step 502 Read in an engine torque Te1 before speed change (when        maintaining the first gear);    -   Step 503 Compute a power output shaft torque Tout1 before gear        change (at the first gear) from the engine torque Te1 read at        Step 502;    -   Step 504 Based on the result of a computation of the power        output torque Tout1 at Step 503, compute a FF (feed forward)        target torque Tc_ff of the assist clutch 6.        -   At this step, assuming that a transmission ratio for the            first gear is R1, a transmission ratio for the second gear            is R2, an engine rotation frequency before gear shift is            Ne1, and an engine rotation frequency after gear shift to            the second gear is Ne2, the engine rotation frequency after            gear shift Ne2 is presumed as in the formula            Ne2≈Ne1×(R2/R1). The engine torque after the gear shift            depends upon the presumed engine rotation frequency Ne2 and            the degree of throttle release (throttle opening), and this            permits a power output shaft torque Tout2 after the gear            shift to be similarly predicted. The FF target torque Tc_ff            of the assist clutch 35 depends upon the prediction Tout2.            Alternatively, the FF target torque Tc_ff of the assist            clutch 35 may be continually computed from the detected            engine rotation frequency Ne and the detected engine torque            Te to satisfy a requirement of transmission period as            specified for various driving situations. Also,            alternatively, the FF target torque Tc_ff of the assist            clutch 6 may be computed from torque components            corresponding to the engine torque continually presumed or            detected, and from inertia torque components required to            reduce the engine rotation frequency in a predetermined            period of time to some rotation frequency level determined            by a gear ratio after the gear shift.    -   Step 505 Determine if a ratio Rch of the engine rotation        frequency Ne (a power input shaft rotation frequency Nin) to the        power output shaft rotation frequency No falls within a        predetermined range. If not, the procedure advances to Step 506,        or if so, the procedure advances to Step 507.    -   Step 506 In the course of the gear shift, when the power        input/output rotation frequency ratio Rch does not fall within        the predetermined range, a torque reduction correcting value        Tc_ref is computed by a substitution as in the equation        Tc_ref=Tc_ff.    -   Step 507 During shift, when the power input/output rotation        frequency ratio Rch falls within the predetermined range, a        frequency ratio FB (feedback) target torque Tc_fb of the assist        clutch 6 is computed by feeding back a deviation of the power        input/output shaft rotation frequency ratio Rch from the target        rotation frequency ratio, which is equivalent to the        transmission ratio for the second gear. Alternatively, the        target engine rotation frequency (power input shaft rotation        frequency) may be computed corresponding to the target rotation        frequency ratio, and then the rotation frequency FB target        torque Tc_fb of the assist cutch 6 may be computed by feeding        back the engine rotation frequency Ne. Also, alternatively, the        target rotation frequency (power input shaft rotation frequency)        during gear shift may be computed by sequentially updating the        gear ratio to bring about a smooth transition of the gear ratio        between before and after the gear shift.    -   Step 508 Compute a commanded transmission torque Tc_ref of the        assist clutch 6 during the gear shift by a substitution as in        the equation Tc_ref=Tc_ff+Tc_fb.    -   Step 509 The commanded transmission torque Tc_ref of the assist        clutch 6, which is respectively obtained at Step 506 and Step        508, is output as the target transmission torque of the assist        clutch 6. From a value of the commanded transmission torque        Tc_ref thus obtained, the actuator 226 adjust pressing force of        the assist clutch 6 as required to optimize the transmission        torque in the course of the gear shift.

Transmitting the torque to the power output shaft 223 with anintervention of the assist clutch 6 during the gear shift in such amanner enables transmission performance to enhance.

The control instruction to the engine 101 during the gear shift will beexplained.

Control instruction follows and executes a program that is stored in amicrocomputer built in the transmission control unit 403.

FIG. 10 is a flow chart illustrating controls over arithmetic operationson control instructions to the engine 101. The program starts with aninterruption of a fixed time interval (e.g., 10 ms) and executes acommand sequence.

-   -   Step 601 Determine if a rate Rch of the engine rotation        frequency Ne (a power input shaft rotation frequency Nin) to the        power output shaft rotation frequency No falls within a        predetermined range. If not, execute torque control procedure 1        at Step 602, or if so, execute torque control procedure 2 at        Step 603.

First, the contents of the procedure of the torque control 1 will beexplained in Step 602 through Step 604 below.

-   -   Step 602 Read the value of the commanded transmission torque        Tc_ref of the assist clutch 6, which is obtained based on the        equation Tc_ref=Tc_ff.    -   Step 603 From the commanded transmission torque Tc_ref obtained        at Step 602, compute an engine target torque Te_ref1 that        achieves the engine rotation frequency Ne required to attain the        predetermined power input/output shaft rotation frequency rate        Rch.    -   Step 604 Output the engine target torque Te_ref1 obtained in        Step 603 and transfer the engine target torque Te_ref1 thus        produced to the electronically controlled throttle controller        401 through the CAN.

The electronically controlled throttle controller 401 regulates theelectronically controlled throttle 103 so as to satisfy the requiredengine target torque Te_ref1.

In addition to that, in order to attain the engine target torqueTe_ref1, an air-fuel ratio of the engine 101 may be adjusted, orotherwise, the ignition timing may be controlled.

As has been described, the controls over the power input shaft rotationfrequency during the gear shift permits the cogged clutch to maintainengagement at the second gear, and the associated control over theinertia torque during the engagement with the second gear enables thetransmission performance to enhance. Also, since the commandedtransmission torque of the assist clutch 6 depends on the torque of theengine 101, such a variability of the transmission torque of the assistclutch 6 allows for adjustment of the power output shaft torque.

Next, the procedure for torque control 2 will be explained in Step 605through Step 607.

-   -   Step 605 Read the commanded transmission torque Tc_ref of the        assist clutch obtained based on the equation Tc_ref=Tc_ff+Tc_fb.    -   Step 606 From the commanded transmission torque Tc_ref obtained        at Step 605, compute the engine target torque Te_ref2 that,        after the gear shift, enables to reduce deviation of the power        output shaft torque from the commanded transmission torque        Tc_ref.    -   Step 607 Output the engine target torque Te_ref2 obtained at        Step 606 and transfer the engine target torque Te_ref2 thus        produced to the electronically controlled throttle controller        401 via the CAN.

The electronically controlled throttle controller 401 regulates theelectronically controlled throttle 103 so as to satisfy the requiredengine target torque Te_ref2.

In addition to that, in order to attain the engine target torqueTe_ref2, an air-fuel ratio of the engine 101 may be adjusted, orotherwise, the ignition timing may be controlled.

As has been described, the controls over the power input shaft rotationfrequency at the end of the gear shift permits a reduction of adeviation of the power output shaft torque after the gear shift from thecommanded torque of the assist clutch 6 during gear shift, and thus, areduced instantaneous rise or drop of the torque enables thetransmission performance to enhance.

Then, an operation during the gear shift from the first gear to thesecond gear will be described.

FIG. 11 is a timing chart illustrating varied states of controlsthroughout the gear shift. In FIG. 11, the speed change instruction Ss,the shift lever position Ii equivalent to the cogged clutch engagementposition, the power input/output shaft rotation frequency rate Rch, thedegree of throttle release θ, the torque Tc of the assist clutch 6, andthe power output shaft torque Tout are respectively denoted at (A)through (F). The horizontal axis of the graph represents time.

As shown in FIG. 11(A), when the speed-change instruction Ss is at Pointa while driving at first gear, gear shift to the second gear is started.Then, as can be seen in FIG. 11(E), the torque Tc of the assist clutch 6gradually increases.

As the torque Tc of the assist clutch 6 rises, the torque Tout of thepower output shaft gradually decreases, as shown in FIG. 11(F), and itis apparent that the cogged clutch that has been connected to the firstgear is capable of disengagement at Point b.

When the cogged clutch is ready for release from the first gearengagement, the actuator 221 permits the cogged clutch to be released,and as can be seen in FIG. 11(B), the shift lever position Ii comes toNeutral (for shifting gear) and an actual gear shift is started.

With the shift lever position Ii in Neutral, as will be recognized inFIG. 11(E), a control over the assist clutch 6 is started to correct thetorque reduction during the gear shift, and the actuator 226 is placedunder control based on the target torque Tc_ref=Tc_ff of the assistclutch 6 that is obtained through the processing routine on the assistclutch transmission torque control command, so as to implement theoptimized torque of the power output shaft in the course of the gearshift.

Since the torque transmitted from the assist clutch is realized as thepower output shaft torque, it is preferable that the target torqueTc_ref of the assist clutch 6 has a smooth property so as to reducediscomfort of driver and passengers. During the gear shift, the rotationfrequency ratio Rch of the power input shaft to the power output shaftalso needs to be shifted quickly and smoothly to the transmission ratioR2 for the second gear.

Thus, in order to attain the engine target torque Te_ref1 that isproduced as a result of the procedure of the torque control 1, as shownin FIG. 11(D), the degree of throttle release θ is regulated to satisfythe requirement expressed as θ=θ_ref1 to perform the torque control overthe engine 101. Consequently, the engine rotation frequency Ne isvaried, and this causes the power input/output shaft rotation frequencyratio Rch to approximate the second gear transmission ratio R2.

The controls over the assist clutch 6 and the electronically controlledthrottle 103 permit the power input/output shaft rotation frequencyratio Rch to reach a level as expressed in Rch=R2 at Point c, but inorder to have an engagement of the cogged clutch, it is desirable thatthe engine rotation frequency Ne is regulated to increase while therotation frequency rate Rch reaches the second gear transmission ratioR2. This is because, to cope with a problem that the engagement of thecogged clutch is interfered with the torque when the rotation frequencyof the power input shaft tends to decrease whereas the rotationfrequency of the power output shaft No is increased due to the commandedtransmission torque of the assist clutch 6 determined through thearithmetic operation during the gear shift, the rotation frequency ofthe power input shaft is managed to increase so that the engagement ofthe cogged clutch undergoes less interference with the torque.

Beyond Point c where Rch<R2, the rotation frequency rate Rch must beincreased. Immediately before the engagement of the cogged clutch (i.e.,between Point c to Point d), however, there arises a slight responsedelay to the control over the engine torque Te, and therefore, it isdesirable that the rotation frequency rate Rch is adjusted by varyingthe torque of the assist clutch 6. Thus, during a period from Point c toPoint d, the target torque of the assist clutch 6 is added by therotation frequency ratio FB target torque Tc_fb of the assist clutch 6that depends on the deviation of the rotation frequency ratio Rch fromthe second gear transmission ratio to the initial target torque of theassist clutch 6, so as to be expressed in the equationTc_ref=Tc_ff+Tc_fb.

In this way, by feeding back the rotation frequency ratio only during aperiod of time when the deviation of the rotation frequency ratio Rchfrom the second gear transmission ratio R2 is relatively small, avariation in the commanded transmission torque during the gear shift canbe minimized, and the driver and passengers can experience a moreconfortable ride. Such a rotation frequency ratio FB control over theassist clutch 6 brings about an optimized condition as expressed inRch≈R2 where the rotation frequency Rch keeps increased, and thispermits the engagement of the cogged clutch to the second-shift gear.

When the cogged clutch is capable of second gear engagement, theactuator 221 is placed under control to effect the engagement of thecogged clutch to the second gear. At this point of time, however, it isdesirable to minimize the deviation of the torque of the power outputshaft after the gear shift (i.e., after connected to the second gear)from the commanded transmission torque of the assist clutch 6 in thecourse of the gear shift so as to reduce the instantaneous rise or dropof the torque of the power output shaft at the end of the transmission.

Although the commanded transmission torque during the gear shift dependson the torque Tc of the assist clutch 6 while the same torque after thegear shift depends on the engine torque Te and the second geartransmission ratio R2, it is necessary that, during Point c and Point d,the throttle opening is adjusted as expressed in the equation θ=θ_ref2to attain the engine target torque Te_ref2. During the gear shift, theassist clutch 6 is loose, and when the engine 101 has its torque Tehigher than its predetermined level, the commanded transmission torqueduring the gear shift depends on the torque Tc of the assist clutch 6.Hence, the torque adjustment after the gear shift can be independent ofthe transmission torque controls over the assist clutch that is carriedout during the gear shift.

After the second gear engagement of the cogged clutch at Point d andonce the speed change is practically completed, the throttle opening θis returned to its initial position prior to the gear shift, and thetransmission control is terminated at Point e.

As stated above, in this embodiment, the torque reduction correctingvalue of the power output shaft is computed during the gear shift, andfrom the resultant correcting value, the rotation frequency of the powerinput shaft is controlled and the torque of the power input shaft isadjusted at the end of the gear shift, thereby retraining a variation inthe torque of the power output shaft.

According to the embodiment of the present invention, the assist clutch6 assists the rotation to the power output shaft 323 under thenon-engaged condition during gear change from the first gear to thesecond gear, from the second gear to the third gear, from the third gearto the fourth gear, and from the fourth gear to the fifth gear, so thatthe accelerating power is transmitted to the power output shaft 323during accelerated but non-engaged condition, resulting in moderatingthe shock the driver feels as if the vehicle is decelerated. That is,even when a mesh-type transmission provided with a clutch for engagingand disengaging the transmission gear and the power output shaft isused, the shock originated from engagement and disengagement of theclutch during acceleration could be relieved.

Also, according to the present embodiment, a mesh-type transmission fortransmitting power of the power input shaft 300 to the power outputshaft 323 by engaging the plurality of cogged clutches 302, 305, 308with the plurality of transmission gears 301, 303, 304, 306, 310 isused, and the automatic transmission, which performs automatic gearchange by controlling engagement of the plurality of cogged clutches302, 305, 308 for engaging and disengaging the voluntary transmissiongears 301, 303, 304, 306, 310 with the power output shaft 323 to thetransmission gear determined from the accelerator command value and thecar speed, is provided with the assist mechanism for transmittingrotational force of the power input shaft 300 to the power output shaft323, when no cogged clutch is engaged with any of above-mentionedplurality of transmission gears during switching of the cogged clutch.Therefore, the shock originated from engaging and disengaging of theclutch during acceleration could be relieved.

Moreover, according to the present embodiment, a mesh-type automatictransmission equipped with the plurality of transmission gears 301, 303,304, 306, 310 provided so as to rotate freely to the power output shaft323 for providing driving force to the wheels, the plurality of coggedclutches 302, 304, 308 connecting with the power output shaft 323, andthe plurality of counter transmission gears 314, 316, 317, 318, 322corresponding to each speed, which are fixed to the counter shaft 315rotated by the rotation of the power input shaft 300 rotated from thepower of the engine 2, and which mesh with the plurality of transmissiongears 301, 303, 304, 306, 310, for performing automatic gear change bycontrolling engagement of the plurality of cogged clutches 302, 305, 308with the voluntary gears 301, 303, 304, 306, 310 of the plurality ofgears 301, 303, 304, 306, 310 determined from the accelerator commandvalue and the car speed, is used. The automatic transmission is providedwith the assist mechanism for assisting transmission of the rotationalforce of the power input shaft 300 to the power output shaft 323 via theassist gear 324 which rotates from the rotation of the counter shaft315, during non-engagement when no cogged clutch of the plurality ofcogged clutches 302, 305, 308 is engaged with any of the plurality ofgears 301, 303, 304, 306, 310, occurring during switching when anengaged cogged clutch of the plurality of cogged clutches 302, 305, 308is disengaged and one of the cogged clutch of the plurality of coggedclutches 302, 305, 308 is to be engaged. Therefore, duringnon-engagement when the cogged clutch and the transmission gear isdisengaged during switching of the transmission gear, the rotation ofthe power input shaft 300 (counter shaft 315) could be assisted to thepower output shaft 323, so that shock originated by engaging anddisengaging of clutch during acceleration could be relieved, even when amesh-type transmission provided with clutches for engaging anddisengaging the gears 301, 303, 304, 306, 310 with the power outputshaft 323 is used.

Furthermore, according to the present embodiment, the position forproviding the counter shaft 315 is formed so as to be positioned belowthe horizontal plane including the central axis of the power outputshaft 323, so that the assist mechanism could be provided to thelowermost portion of the transmission case 30, enabling effective use ofthe interior space of the transmission case, as well as enablingexpectance for cooling effect from the oil. Moreover, the assistmechanism could be mounted to a position without obstructing the accessto the gear oil injection hole.

Still further, according to the present embodiment, the assist clutch 6is provided to the side end portion of the counter shaft 315 at therearward side of the car body, so that the assist clutch 6 could bemounted to position with ease when abnormality occurs to the assistclutch 6, and repairing, replacing and the like of the assist clutch 6is facilitated.

Still further, by mounting the assist clutch 6 to the counter shaft 315,the size of the transmission case 30 could be reduced, and the structureof the automatic transmission 3 could be miniaturized.

As has been recognized in the aforementioned embodiment, the torquetransmission cooperatively carried out by the assist gear 324, theassist output gear 325, and the assist clutch 6 can effectively relievethe shock that occurs during gear shift caused by engagement anddisengagement of the cogged clutches 302, 305, and 308. The torquetransmitted to the power output shaft 323 during the gear shift dependson the assist clutch 6, the assist gear 324, and the assist output gear325. Thus, for practical selection and incorporation into the gear box,the assist gear 324 and the assist output gear 325 must be appropriatelyexamined in view of performance and durability. Selections of the assistgear 324 and the assist output gear 325 will be described below.

FIGS. 12 to 16 shows key properties utilized to select gears of theassist gear 324 and the assist output gear 325 according to the presentinvention. Selection parameters for the gears can be expressed by a gearratio of the assist gear 324 to the assist output gear 325. Atransmission gear ratio among the power input shaft 300, the countershaft 315, and the power output shaft 323 incorporated in thetransmission can be expressed by a product of a gear ratio of the drivegear 301 of the power input shaft 300 to the counter drive gear 314 ofthe counter shaft 315, multiplied by a gear ratio of the gears of thecounter shaft 315 (the counter third-shift gear 316, the countersecond-shift gear 317, the counter first-shift gear 318, and the counterfifth-shift gear 322) to the gears of the power output shaft 323 (thethird-shift gear 303, the second-shift gear 304, the first-shift gear306, and the fifth-shift gear 310).

In contrast to an ordinary transmission gear ratio, we will now explaina method of selecting the assist gear 324 and the assist output gear 325where a gear ratio (referred to as “assist gear ratio” hereinafter) is aproduct of a gear ratio of the assist gear 324 to the assist output gear325 multiplied by a gear ratio of the drive gear 301 to the counterdrive gear 314.

The assist gear ratio affects torque transmitted from the power inputshaft 300 to the power output shaft 323 during the gear shift as well asa differential rotation frequency between the input and output of theassist clutch 6 used to transmit the torque, and hence, transmissionproperties in relation with the assist clutch such as a transmissionenabled zone, transmission performance, durability, and the like varydepending on the assist gear ratio. In this sense, the determination ofthe assist gear ratio is a critical matter.

FIG. 12 shows a relation between the assist gear ratio with thetransmission enabled zone. The vertical axis represents a rotationfrequency ratio (a ratio between a rotation frequency of the power inputshaft 300 to a rotation frequency of the power output shaft 323) whilethe horizontal axis represents the assist gear ratio. The gear ratio isassumed herein as 3.321 for the first gear, 1.902 for the second gear,1.308 for the third gear, 1.000 for the fourth gear, and 9.759 for thefifth gear. As stated above, engagement force of the assist clutch 6 iscontrolled during the gear shift, and the transmission is effected afterraising or dropping the rotation frequency ratio from the power inputshaft 300 to the power output shaft 323 to correspond to the target gearratio. Thus, once specifying the assist gear ratio for the third gear,gearshift using the assist clutch 6 is limited to those from first tosecond, from first to third, and from second to third since the rotationfrequency ratio of the power input shaft 300 to the power output shaft323 cannot be smaller than the gear ratio for the third gear.

On the other hand, once specifying the assist gear ratio for the fifthgear, gearshift using the assist clutch 6 is applicable to all up-shiftsfrom first through fifth. As will be recognized, the transmissionenabled zone is confined within the limits of the assist gear ratio.

Taking the torque transmitted to the power output shaft 323 intoconsideration, before the gear shift, transmission of the engine torqueto the power output shaft 323 is performed relying on a gear ratio of aspecified gear to which the cogged clutches 302, 305, and 308 areengaged. After starting the gear shift, when the cogged clutches 302,305, and 308 are released, the engine torque is transmitted to the poweroutput shaft 323 due to the assist gear ratio. Thus, at the start andend of the gear shift, there arises an instantaneous rise and drop ofthe torque that depends on the difference between the gear rate of thespecified gear before and after the gear shift and the assist gearratio.

Thus, when the assist gear ratio is set equal to a small gear ratio forthe fastest gear, the power output shaft 323 during the gear shift isreduced in torque to produce a large variation from the torque after thegear shift, which causes the shock due to transmission. This torquevariation of the power output shaft 323 is called “differential torque”.

FIG. 13 shows a relation of the assist gear ratio with the torque of thepower output shaft 323. The upper vertical axis represents a rotationfrequency ratio while the lower vertical axis represents a torque of thepower output shaft 323, and the horizontal axis represents the rotationfrequency ratio and the torque of the power output shaft 323 when thegear is shifted from the first gear to the fifth gear. Solid linedenotes the torque of the power output shaft 323 when the assist gearratio is equivalent to the gear ratio for the third gear while brokenline denotes the torque of the power output shaft 323 when the assistgear ratio is equivalent to the gear ratio for the fifth gear. Theengine torque is constant at 200 [Nm]. During the gear shift from firstto second, the differential torque is 118 [Nm] with the assist gearratio equivalent to the gear rate for the third gear, which is 228 [Nm]with the assist gear ratio equivalent to the gear ratio for the fifthgear. During the gear shift from third to fourth, since there arises notorque transmission by the assist clutch 6 with the assist gear ratioequivalent to the third gear, the differential torque is 200 [Nm], whichis 48 [Nm] with the assist gear ratio equivalent to the fifth gear. Ingeneral, although the driver and passengers encounter almost nounpleasantness when the vehicle acceleration rate is around 0.1 [G],they experience unpleasantness when the acceleration rate equals 0.2 [G]or more. Since 100 [Nm] is almost equal to the 0.1 [G] vehicleacceleration rate, the differential torque is desirably 100 [Nm] orless. As has been recognized, the assist gear ratio should not bereduced too much to restrain the shock due to the transmission.

FIG. 14 shows the relation of the gears and the differential torque withthe varied assist gear ratio. The vertical axis represents thedifferential torque while the horizontal axis represents timing of gearshift. Two-dot chain line, solid line, chained line, and broken linerespectively denote the differential torques with the assist gear ratioequivalent to the gear ratio for the second, third, fourth, and fifthgears, respectively. The engine torque is constantly 200 [Nm]. With anylevel of the assist gear ratio, there necessarily is a peak of thedifferential torque. When translated into the practical zone, the gearshift at a high engine torque reaching 200 [Nm] occurs frequently duringtransition from the first to the second and from the second to thethird, but it almost does not occur from the third to the fourth norfrom the fourth to the fifth. Gear shift from the third to the fourthand from the fourth to the fifth is often performed with a low enginetorque. This means that the differential torque for the gear shift fromthe third to the fourth and from the fourth to the fifth is smaller inthe practical zone. In other words, the differential torque for thevelocity shift from the first to the second and from the second to thethird is important. During the gear shift from the first to the second,the differential torque becomes greater with the assist gear ratio forthe fourth and fifth gears, resulting in a poor transmissionperformance, and therefore, it is preferred that the assist gear ratiois kept larger than that equivalent to the gear ratio for the secondgear but smaller than that equivalent to the gear ratio for the fourthgear. However, with the assist gear ratio smaller than that equivalentto the gear ratio for the third gear (e.g., with the assist gear ratioequivalent to the second gear ratio), the gear shift from second tothird is inadequate to the torque transmission by the assist clutch 6,resulting in a poor transmission performance. Thus, to attain asatisfactory transmission performance, it is preferred to use the assistgear ratio greater than the third gear rate but smaller than the fourthgear ratio.

FIG. 15 shows the relation between the assist gear ratio and thedifferential assist clutch rotation frequency. The vertical axisrepresents the differential assist clutch rotation frequency while thehorizontal axis represents the rotation frequency of the power inputaxis 300. Provided that two-dot chain line, solid line, chained line,and broken line respectively denote the differential assist clutchrotation frequency with the assist gear ratio equivalent to the gearratio for the second, third, fourth, and fifth gears, respectively, thedriving at the first and fifth gears are simulated. In this simulation,the differential assist clutch rotation frequency is a variation in therotation frequency from an input to an output of the assist clutchduring the driving at the fixed gear without gearshift, which iscalculated by the following formula:

(Rotation  frequency  of  the  power  input  shaft  300) − (Rotation  frequency  of  the  power  output  shaft  323/Engaged  Gear  Ratio) × (Assist  Gear  Ratio).A large amount of this variation may cause friction of the assist clutchand hence deteriorate the durability thereof. Driving at the first gearpermits driving throughout the zones covering the lowest rotationfrequency of the power input shaft to the highest thereof. Durabilitywould be impaired when the power input shaft 300 rotates at a higherrate with the assist gear ratio equivalent to the gear ratio for thefourth and fifth gears. The rotation frequency of the power input shaft300 during driving at the fifth gear would hardly exceed 4000 [rpm], butinstead, the differential assist clutch rotation frequency almostreaches −6000 [rpm] with the assist gear ratio equivalent to the gearratio for the second gear, which adversely affects the durability of theassist clutch. As the assist gear ratio is reduced, the frequency ofusing the assist clutch is decreased, and hence, its durability is notimpaired.

Simulation and analysis results are shown in FIG. 16. Although theassist gear ratio is advantageously equivalent to the gear rate for thehigher gear for the transmission enabled zone, a contemplation of thetransmission performance and durability of the assist clutch draws amore preferable conclusion that the assist gear ratio should beequivalent to the third gear ratio.

The assist gear ratio can be set equivalent to the third gear ratio.Alternatively, the assist gear ratio may be smaller than the third gearratio; e.g., it may take an intermediate value between the third andfourth gear ratios. In such a case, it becomes possible that a rotationfrequency ratio of the power input shaft 300 to the power output shaft323 is smaller than the third gear ratio during the gear shift fromsecond to third, and the transmission can attain the same level oftransmission performance as it would during the gear shift from thefirst to the second.

With the assist gear ratio equivalent to the third gear, the assistclutch may also serve as a fail-safe mechanism where it enables thevehicle to start at the third gear position when a driveaway clutch isbroken.

Although the exemplary settings of the assist gear ratio have beendescribed in the transmission with five gears, the similar concept canapply to any transmission having less than five gears or more than sixgears.

FIG. 17 depicts a case of a five gear transmission, showing a structureof the transmitter using the assist gear ratio equivalent to the thirdgear ratio. In FIG. 17, the assist gear 324, the assist output gear 325,the drive gear 301 and the counter drive gear 314 are cooperativelyconfigured to attain the third gear ratio. Alternatively, it is alsopossible that the assist gear 324 and the assist output gear 325 areconfigured to attain an intermediate gear ratio between the third andfourth gear ratios. In FIG. 17, although the assist gear 324, the assistoutput gear 325 and the assist clutch 6 are cooperatively transmittingthe torque from the power input shaft 300 to the power output shaft 323,the cogged clutch 320, when responding to the assist gear ratioequivalent to the third gear in the ordinary driving at the third gear,causes the third gear 303 to be engaged with the power output shaft 323,and then the counter third gear 316 and the third gear 303 are joined toperform the driving at the third gear without using the assist clutch 6in any task other than the torque transmission during the gear shift,which is advantageous in enhancing the durability of the clutch. Whenthe cogged clutch for engaging the third gear 303 with the power outputshaft 323 is broken, the assist clutch 6 can be used in substitution forthe third gear to implement the third gear driving.

FIG. 18 is a diagram showing another exemplary structure of thefive-gear transmission used with the assist gear ratio equivalent to thethird gear ratio. In FIG. 18, the assist gear 324, the assist outputgear 325, the drive gear 301 and the counter drive gear 314 arecooperatively configured to attain the third gear ratio. In thisembodiment, the fifth gear is removed from the location taught in theembodiment of FIG. 17, and instead it is located in the position wherethe third gear lies in FIG. 17.

In the arrangement of FIG. 18, the assist clutch 6 may be used for anytask other than the torque transmission during the gear shift; that is,it may be completely engaged during third gear drive to cause the assistgear 324 and the assist output gear 325 to join and implement the thirdgear driving. The assist gear can be commonly used as an ordinarydriving gear as can be seen in FIG. 18, and thus, the number of thegears in the transmission can be reduced.

APPLICABILITY IN THE INDUSTRY

As has been mentioned above, a structure and mechanism according to thepresent invention relieves the shock caused by the clutch being engagedand disengaged during acceleration.

1. A mesh-type automatic transmission, comprising a power input shaftfor introducing engine power, a plurality of transmission gears, aplurality of cogged clutches, a power output shaft for outputtingdriving force, a counter shaft, and a plurality of counter gears fortransmitting the engine power to said power output shaft by rotatingsaid power input shaft via the engine power, rotating said counter shaftby rotation of said power input shaft, and transmitting rotation of saidcounter shaft to said power output shaft via said counter gearautomatically by engaging and disengaging said cogged clutch to one ofsaid transmission gears corresponding to speed; wherein said countershaft is provided with an assist mechanism for transmitting rotationalforce of said power input shaft to said power output shaft bytransmitting rotation of said counter shaft via said assist mechanismduring a gear change from the time of disengagement of a gear to theengagement of a new gear, said assist mechanism including an assistclutch having an assist counter shaft, an assist gear associated androtatable with said assist counter shaft, and an assist output gearoperatively associated with the power output shaft, wherein said assistmechanism starts engaging when a switch command of said cogged clutch isoutput before said cogged clutch currently engaged with saidtransmission gear is completely disengaged, transmits the rotationalforce of said power input shaft to said power output shaft by beingengaged corresponding to the torque of the engine when said coggedclutch is completely disengaged from said engaged transmission gear, anddisengages when said cogged clutch is engaged with said transmissiongear to be engaged based on said switch command.
 2. An automatictransmission according to claim 1, wherein said assist mechanism isprovided to the lateral rear end portion of said counter shaft in a carbody.
 3. An automatic transmission according to claim 2, wherein saidassist mechanism is provided below a horizontal plane where a centeraxis of said power output shaft lies.
 4. A mesh-type automatictransmission equipped with a power input shaft for introducing power ofan engine, a power output shaft for outputting the driving force of thetransmission, a counter shaft receiving the driving force that istransmitted from the power input shaft through a series of power inputgears, a series of power output gears disposed between the counter shaftand the power output shaft, and cogged clutches provided between theseries of power output gears and the power input shaft and between thosepower output gears and the power output shaft, the power of the enginebeing transmitted from the power input shaft to the power output shaftby the engagement and disengagement of the cogged clutches, wherein theautomatic transmission comprises an assist mechanism, the assistmechanism including an assist counter gear that is provided on thecounter shaft and adapted for idling rotation, an assist output gearmeshed with the assist counter gear and fixed to the power output shaft,and a friction clutch that is provided between the assist counter gearand the counter shaft to transmit the driving force from the countershaft to the power output shaft via the assist counter gear and theassist output gear while the cogged clutches are being switched fromengagement to disengagement and vise versa.
 5. An automatic transmissionaccording to claim 4, wherein the assist mechanism is provided to thelateral rear end portion of said counter shaft in a car body.
 6. Anautomatic transmission according to claim 4, wherein said assistmechanism is provided below a horizontal plane where a center axis ofsaid power output shaft lies.
 7. A mesh-type automatic transmissionequipped with a power input shaft for introducing power of an engine, apower output shaft for outputting the driving force of the transmission,a counter shaft receiving the driving force that is transmitted from thepower input shaft through a series of power input gears, a series ofpower output gears disposed between the counter shaft and the poweroutput shaft, and cogged clutches provided between the series of poweroutput gears and the power input shaft and between those power outputgears and the power output shaft, the power of the engine beingtransmitted from the power input shaft to the power output shaft by theengagement and disengagement of the cogged clutches, wherein theautomatic transmission comprises an assist mechanism, the assistmechanism including an assist counter gear that is provided on thecounter shaft and adapted for idling rotation, an assist output gearmeshed with the assist counter gear and fixed to the power output shaft,and a friction clutch that is provided between the assist counter gearand the counter shaft to transmit the driving force from the countershaft to the power output shaft via the assist counter gear and theassist output gear while the cogged clutches are being switched fromengagement to disengagement and vise versa.
 8. An automatic transmissionaccording to claim 7, wherein the assist mechanism is provided to thelateral rear end portion of said counter shaft in the car body.
 9. Anautomatic transmission according to claim 7, wherein said assistmechanism is provided below a horizontal plane where a center axis ofthe power output shaft lies.
 10. A mesh-type automatic transmission,comprising a power input shaft for introducing engine power, a pluralityof transmission gears, a plurality of cogged clutches, a power outputshaft for outputting driving force, a counter shaft, and a plurality ofcounter gears for transmitting the engine power to said power outputshaft by rotating said power input shaft via the engine power, rotatingsaid counter shaft by rotation of said power input shaft, andtransmitting rotation of said counter shaft to said power output shaftvia said counter gear automatically by engaging and disengaging saidcogged clutch to one of said transmission gears corresponding to speed;wherein said counter shaft is provided with an assist mechanism fortransmitting rotational force of said power input shaft to said poweroutput shaft by transmitting rotation of said counter shaft via saidassist mechanism during a gear change from the time of disengagement ofa gear to the engagement of a new gear, said assist mechanism includingan assist clutch having an assist counter shaft, an assist gearassociated and rotatable with said counter assist shaft, and an assistoutput gear operatively associated with the power output shaft, whereinthe assist mechanism responds to a switch command for the coggedclutches and starts transmitting the power from the engine to the poweroutput shaft prior to complete release of one of the cogged clutchesthat is currently engaged with the transmission gear; the assistmechanism transmits torque in accordance with the power from the enginewhen the cogged clutch is completely released and disengaged from thetransmission gear; and the assist mechanism terminates transmitting thepower to the power output shaft when the cogged clutch is engaged withthe transmission gear based on said switch command.
 11. An automatictransmission according to claim 10, wherein said assist mechanism isprovided to the lateral rear end portion of said counter shaft in thecar body.
 12. An automatic transmission according to claim 11, whereinsaid assist mechanism is provided below a horizontal plane where acenter axis of said power output shaft lies.
 13. An automatictransmission according to claim 12, wherein said assist mechanism startsengaging when a switch command of said cogged clutch is output beforesaid cogged clutch currently engaged with said transmission gear iscompletely disengaged, transmits the rotational force of said powerinput shaft to said power output shaft by being engaged corresponding tothe torque of the engine when said cogged clutch is completelydisengaged from said engaged transmission gear, and disengages when saidcogged clutch is engaged with said transmission gear to be engaged basedon said switch command.
 14. A mesh type automatic transmissioncomprising a power input shaft for introducing engine power, a pluralityof transmission gears, a plurality of cogged clutches, a power outputshaft for outputting driving force, a counter shaft, and a plurality ofcounter gears for transmitting the engine power to said power outputshaft by rotating said power input shaft via the engine power, rotatingsaid counter shaft by rotation of said power input shaft, andtransmitting rotation of said counter shaft to said power output shaftvia said counter gear automatically by engaging and disengaging saidcogged clutch to one of said transmission gears corresponding to speed;wherein said counter shaft is provided with an assist mechanism fortransmitting rotational force of said power input shaft to said poweroutput shaft by transmitting rotation of said counter shaft via saidassist mechanism during a gear change from the time of disengagement ofa gear to the engagement of a new gear, said assist mechanism includingan assist clutch having an assist counter shaft, an assist gearassociated and rotatable with said assist counter shaft, and an assistoutput gear operatively associated with the power output shaft. whereinsaid assist mechanism is comprised of said assist clutch, which iscomposed of a clutch plate fixed to said counter shaft and rotated withsaid counter shaft for transmitting rotation of said clutch elate bypressing against said clutch plate, and said assist output gear fixed tosaid power output shaft and meshed with said assist gear of said assistclutch, wherein the rotation of said clutch plate is transmitted to saidpower output shaft via said assist gear and said assist output gearbased on an assist command, wherein said assist mechanism is provided tothe lateral rear end portion of said counter shaft in a car body below ahorizontal plane where a center axis of said power output shaft lies,and starts engaging when a switch command of said cogged clutch isoutput before said cogged clutch currently engaged with saidtransmission gear is completely disengaged, transmits the rotationalforce of said power input shaft to said power output shaft by beingengaged corresponding to the torque of the engine when said coggedclutch is completely disengaged from said engaged transmission gear, anddisengages when said cogged clutch is engaged with said transmissiongear to be engaged based on said switch command.
 15. A mesh-typeautomatic transmission, comprising a power input shaft for introducingengine power, a plurality of transmission gears, a plurality of coggedclutches, a power output shaft for outputting driving force, a countershaft, and a plurality of counter gears for transmitting the enginepower to said power output shaft by rotating said power input shaft viathe engine power, rotating said counter shaft by rotation of said powerinput shaft, and transmitting rotation of said counter shaft to saidpower output shaft via said counter gear automatically by engaging anddisengaging said cogged clutch to one of said transmission gearscorresponding to speed; wherein said counter shaft is provided with anassist mechanism for transmitting rotational force of said power inputshaft to said power output shaft by transmitting rotation of saidcounter shaft via said assist mechanism during a gear change from thetime of disengagement of a gear to the engagement of a new gear, saidassist mechanism including an assist clutch having an assist countershaft, an assist gear associated and rotatable with said assist countershaft, and an assist output gear operatively associated with the poweroutput shaft, wherein said assist mechanism starts engaging when aswitch command of said cogged clutch is output before said cogged clutchcurrently engaged with said transmission gear is completely disengaged,transmits the rotational force of said power input shaft to said poweroutput shaft by being engaged corresponding to the torque of the enginewhen said cogged clutch is completely disengaged from said engagedtransmission gear, and disengages when said cogged clutch is engagedwith said transmission gear to be engaged based on said switch command,and a gear ratio of the assist gear is equal to a limit of the gearratio obtained in the plurality of transmission gears.
 16. A mesh-typeautomatic transmission equipped with a power input shaft for introducingpower of an engine, a power output shaft for outputting the drivingforce of the transmission, a counter shaft receiving the driving forcethat is transmitted from the power input shaft through a series of powerinput gears, a series of power output gears disposed between the countershaft and the power output shaft, and cogged clutches provided betweenthe series of power output gears and the power input shaft and betweenthose power output gears and the power output shaft, the power of theengine being transmitted from the power input shaft to the power outputshaft by the engagement and disengagement of the cogged clutches,wherein the automatic transmission comprises an assist mechanism, theassist mechanism including an assist counter gear provided on thecounter shaft and adapted for idling rotation, the assist counter gearbeing different from gears used for ordinary gear shift, an assistoutput gear meshed with the assist counter gear and fixed to the poweroutput shaft, the assist output gear being different from the gears usedfor ordinary gear shift, and a friction clutch provided between theassist counter gear and the counter shaft to transmit the driving forcefrom the counter shaft to the power output shaft via the assist countergear and the assist output gear while the cogged clutches are beingswitched from engagement to disengagement with the gears and vise versa;and a gear ratio of the assist counter gear and the assist output gearis equal to a limit of the gear ratio obtained in the series of powerinput gears and the series of output gears.
 17. A mesh-type automatictransmission equipped with a power input shaft for introducing power ofan engine, a power output shaft for outputting the driving force of thetransmission, a counter shaft receiving the driving force that istransmitted from the power input shaft through a series of power inputgears, a series of power output gears disposed between the counter shaftand the power output shaft, and cogged clutches provided between theseries of power output gears and the power input shaft and between thosepower output gears and the power output shaft, the power of the enginebeing transmitted from the power input shaft to the power output shaftby the engagement and disengagement of the cogged clutches, wherein theautomatic transmission comprises an assist mechanism, the assistmechanism including an assist counter gear provided on the counter shaftand adapted for idling rotation, the assist counter gear being differentfrom gears used for ordinary gear shift, an assist output gear meshedwith the assist counter gear and fixed to the power output shaft, theassist output gear being different from the gears used for ordinary gearshift, and a friction clutch provided between the assist counter gearand the counter shaft to transmit the driving force from the countershaft to the power output shaft via the assist counter gear and theassist output gear while the cogged clutches are being switched fromengagement to disengagement with the gears and vise versa; and a gearratio of the assist counter gear and the assist output gear is equal toa limit of the gear ratio obtained in the series of power input gearsand the series of output gears.